Optical device

Abstract

The optical device, capable of reducing reflectance over a wide wavelength region, has an anti-reflection film interposed between a rod lens and an optical fiber. The anti-reflection film includes a plurality of laminas. The refractive index of the lamina contiguous to the optical fiber is matched with that of the optical fiber, while the refractive index of the lamina contiguous to the rod lens is matched with that of the rod lens. The laminas are set to have refractive indices such that the refractive index of the optical fiber and that of the rod lens are connected to each other to form a smooth curve.

What is claimed is:  
     
         1 . An optical device including a first optical element having a first refractive index and a second optical element having a second refractive index which differs from the first refractive index, wherein light is introduced from the first optical element into the second optical element, the optical device comprising: 
 an anti-reflection film interposed between the first optical element and the second optical element, the anti-reflection film having a first interface opposing the first optical element and a second interface opposing the second optical element, the first interface having a refractive index substantially equal to that of the first refractive index, the second interface having a refractive index substantially equal to that of the second refractive index, wherein the refractive index of the anti-reflection film continuously changes between the first interface and the second interface.    
     
     
         2 . The optical device according to  claim 1 , wherein the anti-reflection film has a refractive index distribution that changes monotonously from the first interface to the second interface and that is expressed by any of a polynomial equation of a higher order and a function tan H.  
     
     
         3 . The optical device according to  claim 1 , wherein the derivatives of the function expressing the refractive index distribution which are zero at the first and second interfaces.  
     
     
         4 . The optical device according to  claim 1 , wherein the anti-reflection film has a thickness of about 1 μm to about 10 μm.  
     
     
         5 . The optical device according to  claim 1 , wherein the difference between the refractive index of the anti-reflection film at the first interface and the first refractive index is 0.01 or less, and the difference between the refractive index of the anti-reflection film at the second interface and the second refractive index is 0.01 or less.  
     
     
         6 . The optical device according to  claim 1 , wherein the first optical element is a gradient index type rod lens having the anti-reflection film formed on one end face thereof, and the second optical element is a single mode optical fiber having a polished end face, the anti-reflection film being bonded to the polished end face.  
     
     
         7 . An optical device including a first optical element having a first refractive index and a second optical element having a second refractive index which differs from the first refractive index, in which light is introduced from the first optical element into the second optical element, the optical device comprising: 
 an anti-reflection film interposed between the first optical element and the second optical element, the anti-reflection film having a plurality of laminas including a first lamina opposing the first optical element and a second lamina opposing the second optical element, wherein the first lamina has a refractive index substantially equal to that of the first refractive index, the second lamina has a refractive index substantially equal to that of the second refractive index, and wherein the refractive index of the anti-reflection film changes monotonously between the first lamina and the second lamina.    
     
     
         8 . The optical device according to  claim 7 , wherein the anti-reflection film has a refractive index distribution that changes monotonously from the first lamina to the second lamina and that is expressed by any of a polynomial equation of a higher order and a function tan H.  
     
     
         9 . The optical device according to  claim 7 , wherein the derivatives of the function are zero at an interface between the first optical element and the first lamina and at an interface between the second optical element and the second lamina.  
     
     
         10 . The optical device according to  claim 7 , wherein the anti-reflection film has a thickness of about 1 μm to about 10 μm.  
     
     
         11 . The optical device according to  claim 7 , wherein the refractive index of the anti-reflection film changes at a rate which is smaller as it approaches the first optical element and the second optical element.  
     
     
         12 . The optical device according to  claim 7 , wherein the difference between the refractive index of the first lamina and the first refractive index is 0.01 or less, and the difference between the refractive index of the second lamina and the second refractive index is 0.01 or less.  
     
     
         13 . The optical device according to  claim 7 , wherein at least one of the first optical element and the second optical element is formed of a material selected from the group consisting of glass, resins, semiconductors and dielectric materials.  
     
     
         14 . The optical device according to  claim 7 , wherein at least one of the first optical element and the second optical element is a lens.  
     
     
         15 . The optical device according to  claim 7 , wherein at least one of the first optical element and the second optical element is an optical fiber.  
     
     
         16 . The optical device according to  claim 7 , wherein the first optical element is a gradient index type rod lens, and the second optical element is an optical fiber.  
     
     
         17 . The optical device according to  claim 7 , wherein at least one of the first optical element and the second optical element is a planer optical waveguide.  
     
     
         18 . The optical device according to  claim 7 , wherein at least one of the first optical element and the second optical element has a passage charged with a liquid or a gas.  
     
     
         19 . An optical device comprising: 
 an optical fiber having a first refractive index;    a rod lens, which is optically bonded to the optical fiber and has a second refractive index; and    an anti-reflection film including a first lamina formed contiguous to the optical fiber and having a refractive index substantially equal to the first refractive index, a second lamina formed contiguous to the end face of the rod lens and having a refractive index substantially equal to the second refractive index, and a plurality of third laminas laminated between the first lamina and the second lamina and having a refractive index which differ from the first and second refractive indices.    
     
     
         20 . The optical device according to  claim 19 , wherein the difference between the refractive index of the first lamina and the first refractive index is 0.01 or less, and the difference between the refractive index of the second lamina and the second refractive index is 0.01 or less.  
     
     
         21 . The optical device according to  claim 20 , wherein the difference between refractive indices of every two adjacent third laminas is constant.  
     
     
         22 . The optical device according to  claim 21 , wherein the anti-reflection film has a thickness of greater than 2000 nm.  
     
     
         23 . The optical device according to  claim 20 , wherein the difference between refractive indices of every two adjacent third laminas reduces toward the first and second laminas.  
     
     
         24 . The optical device according to  claim 23 , wherein the anti-reflection film has a thickness of about 1 μm to about 10 μm.  
     
     
         25 . The optical device according to  claim 19 , having a reflectance of −50 dB or less in a wavelength region of 1300 to 1700 nm.  
     
     
         26 . The optical device according to  claim 19 , wherein each lamina is an optical mixture film formed by means of reactive sputtering using a plurality of target materials.